iMac Freezing

What rom revision is?

I have the same problem. Horizontal lines, crashes when GPU gets hot.
20-inch iMac, 2GHz, early 2006, Mac OS X 10.4.11, ATI RadeonX1600.

I've taken my machine into an Apple store and they are going to get a technician to look at it. The Genius reproduced the problem (the air-conditioning in the store made it run for longer, but it did crash).

Other details that may help to confirm if we all have the same problem:
1) It only crashes if the GPU is being used (i.e. gets hot) - the machine runs perfectly OK as a "server".

2) I installed the "Hardware Monitor" software, which consistently shows that the crashes happen when the GPU temperature gets to 56 degrees centigrade. Given that the CPU can run at much higher temperatures, the GPU should be able to cope with temperatures higher than 56 degrees.

3) I can get the crash to occur easily, within a minute or so, by running 3 QuickTime players at the same time - the GPU temperature goes slowly up and then the crash occurs. It also occurs when running a single QuickTime player in full-screen (but it then takes longer to for the GPU to get hot, so longer before the crash).

4) Sometimes after the crash, the audio of the video being played continues OK, but the video is frozen. The cursor turns into the spinning beachball. The cursor moves with the mouse, but all mouse clicks are ignored. Command-Alt-Esc does not bring up Force Quit.

5) I installed "Fan Control" which did reduce the temperature of the GPU, which made it last longer before crashing (but it still crashed if the GPU got higher than 56 degrees)..

6) I get the following in the system log (which seems to occur with a few other people that have reported similar problems):
Jul 30 23:17:24 Swallow kernel[0]: ATIRadeon::wait for_rbspace: Overflowed block waiting for FIFO space. Have 2, need 5. RBBM_STATUS 0x10000140
Jul 30 23:17:35 Swallow kernel[0]: ** ASIC Hang Log Start **
Jul 30 23:17:35 Swallow kernel[0]: 0x010071c5 00040100 0001fff2 200801b8
Jul 30 23:17:35 Swallow kernel[0]: 0x1b826098 80000004 00000002 00000008
Jul 30 23:17:35 Swallow kernel[0]: 0x00000047 00000000 00002f2f 10000140
Jul 30 23:17:35 Swallow kernel[0]: 0x00080000 00000000 00000001 40000000
Jul 30 23:17:35 Swallow kernel[0]: 0x4000ffff 0004000a 00000000 00800000
Jul 30 23:17:35 Swallow kernel[0]: 0x00000003 0000444f 10040100
Jul 30 23:17:35 Swallow kernel[0]: 0:0x000101ce
Jul 30 23:17:35 Swallow kernel[0]: 1:0x0861c020
.
.
Jul 30 23:17:46 Swallow kernel[0]: 1022:0x01100332
Jul 30 23:17:46 Swallow kernel[0]: 1023:0x4c0361d4
Jul 30 23:17:46 Swallow kernel[0]: 0xea2608fa
Jul 30 23:17:46 Swallow kernel[0]: ** ASIC Hang Log End **

Message was edited by: Woll
Added graphics card spec.

tyc314159 wrote:
What rom revision is?

My ROM Revision on the new card is 3022.

It's very interesting that we seem to be having the same exact type of problem, but very different manifestations of it. I could recreate it by exercising OpenGL functionality, and I see OpenGL errors in my system log. You, on the other hand, also exercise the video card, but in a different way, and get different errors on a different card. Same machines, same heat issue, same basic visual effects (visual artifacts and/or lockup - I get both).

Hmmm...

This reminds me. I don't know if anyone else notices, but every time my machine has crashed, it is only the GUI that crashes. For example, I can still login through SSH and use the machine. As long as you stay away from anything related to graphics it still works.

Doesn't help me much with it being my primary computer... but if it ever "bricks" (and it's a 20", so no cheap upgrade possible), at least I can still use it as a server, for as long as that will last.

Bill Gross wrote:
This reminds me. I don't know if anyone else notices, but every time my machine has crashed, it is only the GUI that crashes. For example, I can still login through SSH and use the machine. As long as you stay away from anything related to graphics it still works.

Doesn't help me much with it being my primary computer... but if it ever "bricks" (and it's a 20", so no cheap upgrade possible), at least I can still use it as a server, for as long as that will last.

Yes, that was the same for me. Whenever it would lock up, I would ssh in and reboot it cleanly, instead of powering it off/on.

How do you pull-off this SSH thing?

Hi,
you can try put the computer to sleep by pressing power button and wait until display dims and light pulses. Sometimes after wake up computer restarts Window Manager and one can save unsaved documents. But restart after such a recover is recomended.

Marek

Zachnap wrote:
How do you pull-off this SSH thing?

If you're familiar with SSH and the terminal it's easy, otherwise it might seem a little imposing.

You're going to need a second computer to login to the frozen one, and it needs to be on the same network as your iMac (e.g., you have your iMac plugged into the ethernet port of your AirPort router, and then you also have a laptop that uses that same router).

Now, you need SSH enabled on your machine (System Preferences->Sharing->Remote Login). When you go to that Preference panel it will have a nice friendly message telling you how to login to your machine. For example, 'To log in to this computer remotely, type "ssh ...".'

Now, to login through SSH you need to go onto a different computer on your network, open up Terminal.app, and type that command that the Prefence panel gave you. If your username is different, you'll need to modify the command to take that into account. For example, if your username on your iMac is "dog", you'll need to type "ssh dog@...".

Once your in, you can do whatever you want from the command-line. For example, to restart the computer, type "sudo shutdown -r now".

Hope that helps. If it's confusing, find your nearest computer nerd.

I knew there was something else I had forgotten!

Yes, after a GPU-card crash I could also still login via SSH (on the 3 times I tried) and reboot it cleanly.

My freezing and screen glitches are definitely related solely to heating and seem to be caused by intensive graphics use.

I installed SMC Fan control and that seems to have solved it for me. Prior to that it would freeze constantly and I am not a high end graphics user. As long as the computer temperature remains below 45, no problems and generally my temperature is well below that -- 40 C max.

The only time I have had a glitch was when a child was visiting and they were playing Snood on the machine. Snood is a pretty basic game but that caused the temperature to rise and the anomalies (tearing screen) to start. I can't imagine what it would be like if I actually wanted to really use the computer for graphics intensive stuff.

It's really a shame that these computers have this issue because a $2000 computer should certainly be able to handle normal use without the heat causing it to crash -- especially an Apple which is touted as being particularly good for graphics.

I think this computer should last for its "normal" life since it's operating fine with my "normal" needs which aren't pushing its graphics limits constantly.

Al, I also have a 24" late '06 iMac with the same issues as everyone else here (posted about it elsewhere). I might be willing to open up the box and either replace the 7600GT (the card I have) or at least clean out the dust. If you have a pointer or link to how to open up the case and get to things that would be very helpful.

In the meantime I have installed smcFanControl, and by boosting the fan speeds to just barely audible I've dropped GPU temps from the mid-50s to the low-40s. So far that has completely solved my problem.

Here's two links:

The first one shows (sort of) how to open up the iMac and replace the graphics card. Remember everyone, only the 24" iMac has a graphics card that can be swapped out, all the other iMacs have a soldered-on graphics card as far as I know.

http://www.techdc.com/imac-24-opened-and-upgraded

This second link is for replacing the HD in your iMac, but it shows quite nicely how to open up the case:

http://home.comcast.net/~woojo/DFFA53A0-F23D-4541-9015-481FD3B6532E/iMac_Disasse mbly.html

And here, posted earlier in the thread by another great user, are step-by-step instructions for the whole process. Be forewarned, this is NOT a simple "pop in the new card" procedure, do this only if you're comfortable with possibly destroying your iMac completely. I personally am, because if this doesn't work I'll have to buy a new one anyways, freaking apple thanks for sticking it to me like that.

Ok, for those who want to do this themselves, here's what you'll need:
* 2006 Intel 24" iMac with borked graphics card
* New graphics card from welovemacs.com (or some other authorized Apple reseller)
* Standard screwdriver set
* Torx screwdriver set
* Table big enough to lay your iMac down
* Bags or bowls to hold screws (label each with the step number)
* These instructions (printed so you can check off the steps, twice)

Step 1: REMOVE THE CASE FRONT
Stand the iMac at the edge of the table and tilt back so that the bottom edge is exposed.

* remove bottom screws (4x torx)
* loosed memory cover screws (2x philips) and remove memory cover
* while keeping the two grey memory tabs "up" in the case, pry the bottom of the case towards you until the bottom edge comes loose
* keep working front of the case until the top comes loose
* find and disconnect the iSight and Mic connectors before pulling the front of the case completely off the iMac
* once the case front is removed, lay the iMac on its back for the remainder of the operation

Step 2: CONDUCTIVE TAPE PEELBACK
On the "bottom corners" of the iMac, there is a small amount of conductive black and silver tape. Gently peel this tape away from the components (speakers and LCD) so that it isn't going to prevent these components from being removed.

Step 3: SPEAKER REMOVAL
Well, you're not going to actually remove the speakers yet, but you need to pull them out from where they are sitting.

* Remove left speaker screw (1x long torx)
* Remove right speaker screw (1x medium torx)
* pull both speakers out, but tuck them between the "bottom" edge of the case and the stand
* DONT TUG ON THE CABLING! we'll get to that later
Step 4: LCD REMOVAL
You may need another person to help hold the LCD while you disconnect two connectors. Please be careful with the delicate LCD screen. You don't want to have to replace that, too!

* Remove screws at the "bottom" edge of the LCD that used to be covered by the speakers (2x long torx)
* Remove screws along the "left" and "right" edges of the LCD (8x short torx)
* Disconnect the "INVERTER" connector at the "bottom" edge of the case, to the left of the memory slots
* Pull out the LCD about 6" or so and locate the cable that is still attached to the panel
* With the LCD in midair, unhook the connector on the underside of the LCD panel (this one gave me a bit of trouble so be careful with it)
* Remove the LCD completely and store it somewhere safe

Step 5: LEFT FAN REMOVAL (THE LONG ONE)
* Disconnect the left fan cable connector
* Remove the left fan (just wiggle and tug until it pops out)

Step 6: RIGHT FAN REMOVAL (THE SHORT ONE)
* Disconnect the right fan cable connector
* Remove the right fan (again, just wiggle and tug)

Step 7: REMOVE RIGHT SPEAKER
* Disconnect the right speaker's cable connector
* Remove the right speaker

Step 8: LOGIC BOARD CONNECTOR DISCONNECTIONS
Quite a few connectors on the logic board to disconnect, so stay sharp and check them off as you go:

* Disconnect "PWR" (tiny, near the INVERTER and left speaker connectors)
* Disconnect wireless antenna connector (black wire near the left speaker connector, wiggle and tug)
* Disconnect "AMBIENT TEMP" (left side of memory modules)
* Disconnect "HD SATA" (near the main power connector, right of the memory modules)
* Disconnect main power (giant black connector)
* Disconnect "COM and MIC" (just to the right of the right fan's connector)
* Disconnect BlueTooth antenna connectors (2x wiggle and tug)
* Disconnect right speaker connector (top right edge of logic board)
* Disconnect "OD TEMP"
* Disconnect OD connector (thin orange plastic connector with tiny embedded wires; be careful!)
* Disconnect "HD BLOWER" ("top" of logic board)
* Disconnect "HD TEMP" ("top" of logic board)

Step 9: LOGIC BOARD SCREW REMOVAL
Remove screws on "bottom" edge of logic board (4x torx)
a. near the INVERTER connection, by the left fan
b. near the main power connector
c. near the HD SATA connector
d. near the "bottom right" edge
Remove screws on the "top" edge of the logic board (1x torx)
e. near the right speaker connector (top right edge)
Remove screws within the metal "framework" on the top of the logic board: (3x torx, with etched arrows pointing to them)
f. near the OD, top right side of the logic board
g. near the middle of the logic board
h. near the heat sinks (top left edge of the logic board)
Remove screws holding the heat sinks in place (2x torx)
i. top left edge of the top heat sink
j. bottom left edge of the bottom heat sink

Step 10: LOGIC BOARD REMOVAL
Almost there! Black sticky tape/foam connects the (covered in black paper) power supply to the heat sinks. It must be removed first:

* Gently peel back the black foam the is stuck to the metal framework on the top edge of the top heatsink
* If you're careful, the black tape/foam shouldn't tear
* Lift out the logic board, flip it over, and set it on a flat surface

Step 11: GRAPHICS CARD REPLACEMENT
You did order a new card, right?

OK, get the logic board situated so that:

* heat sinks are on the bottom left corner
* memory modules are on the top edge
* external connectors are on the top right corner

There are three screws to remove to free the old graphics card:

* on the left side of the bottom heat sink (1x torx)
* on the bottom left and right corners of the graphics card board (2x torx)

Once those are removed, you can wiggle and tug the graphics card board down (towards the bottom edge of the logic board) until the connector comes loose.

To replace the graphics card, just pop the board connectors in and replace the three screws.

Before putting your system back together, you can take this opportunity to improve your iMac's airflow by giving it a good cleaning. I suggest ditching those terrible air cans and just getting a shop vac with a brush attachment.

Also, you have a perfect opportunity here to upgrade your hard drive.

Now, as for the rebuild instructions, just follow the instructions in reverse! Hope this helps someone out there and please let me know if I've made any errors or omissions.

ADDITIONAL INFO

It is not necessary to remove the two screws on the bottom of the LCD panel, behind the speakers. In fact, it's not necessary to take out the left speaker at all.

3. It is also not necessary to remove either of the fans.

4. Before removing the LCD panel, disconnect both the inverter connector, and the LVDS connector (has two T-6 torx screws holding this cable in, and is just to the right of the battery). This way, when you lift up the LCD panel, it will come right out - there's no need to disconnect a cable from the bottom of the LCD panel while you're holding it.

5. m104's instructions remove 10 screws from the logic board, but only 8 are necessary to remove.

Micah -- thanks! That's very helpful indeed!

You're welcome, I just received my new 7600 graphics card yesterday so I'm going to be performing this upgrade some time soon, time permitting. Maybe I'll take pics and post them so as to add my own tutorial.